1. Field of the Invention
The present invention concerns state transitions by a mobile device in a wireless cellular-based communications system, and more particularly concerns transitions to an idle, or base-station-monitoring, state upon completion of a packet data call.
2. Description of the Related Art
Various techniques exist for cellular-based wireless communications systems. Such techniques include code division multiple access (CDMA), time division multiple access (TDMA) and frequency division multiple access (FDMA), as well as techniques which employ different combinations of such multiplexing.
In addition to the basic technology employed, various standards exist for accomplishing mobile wireless communications in a cellular-based system. One example of such standards is IS2000A which provides for voice and data communications in a CDMA environment. According to the IS2000A standard, the mobile unit (e.g., wireless telephone, personal digital assistant or other wireless device) operates in a number of different states in order to perform all tasks related to the desired communications. This is illustrated in FIG. 1.
As shown in FIG. 1, processing begins in power-up state 10 after a user switches on the power for the mobile unit, such as by pressing a power key. Power up may involve preliminary tasks, such as setting registers.
Next, the mobile unit goes into an initialization state 12. In this state, the mobile unit selects a base station to use. Generally, this is accomplished by scanning for signals from nearby base stations and selecting the strongest signal. As a result of this selection, the pilot signal for the base station is acquired. Then, the synchronization information for such base station is acquired, and the mobile unit adjusts its timing so as to synchronize with the selected base station.
Once a base station has been selected in initialization state 12, the mobile unit enters idle state 14 in which the mobile unit monitors the base station, waiting to receive certain overhead information regarding the base station, and then uses such information to calculate channel parameters. According to the IS2000A standard, the base station is only required to transmit its overhead information every 1.28 seconds. Once such overhead information has been received and the channel parameters have been calculated, the mobile unit monitors the base station for an incoming call and also waits for any call that might be initiated by the user. In either case, such calls may be voice calls, i.e., conventional telephone calls. Alternatively, such calls may be data calls, such as calls to send or to receive e-mail or other short text messages or calls to request or to transmit Web pages.
Thus, at the same time that the mobile unit is waiting for a base station request to initiate a call, it also waits for an input from the user to initiate a call. Such user input might include, for example, entry of a telephone number and pressing of a “send” key, or else might include designation of a Web page, or wireless markup language (WML) page, link. It is noted that a user-initiated call may be directly requested by the user or initiated automatically based on a user action. In fact, multiple calls may be automatically initiated by a single user action.
In the access state 16, a request for a call has been received by the mobile unit, either from the base station or from a user, and processing is performed to initiate the call. Such processing typically will include communication of the channel to be used for forward link communications (i.e., from the base station to the mobile unit) and/or communication of a channel to be used for reverse link communications (i.e., from the mobile unit to the base station).
In traffic channel state 18, the call is conducted (e.g., by transmitting packet data or by communicating two-way voice data). Upon completion of the call 18, the previously acquired overhead information is cleared and processing returns to step 12 in order to again acquire a base station to monitor. This return to the initialization state conventionally is considered necessary because the best base station to monitor might have changed during the call.